Seed Plants, Biology tutorial

Introduction:

The spermatophytes, that mean seed plants, are some of the most significant organisms on Earth. Life on land as we all are familiar with it is shaped mainly by the actions of the seed plants. Soils, forests and food are three of the most obvious products of this group. Seed-producing plants are perhaps the most well-known plants to most people, dissimilar to liverworts, mosses, horsetails and most other seedless plants that are unnoticed because of their size or subtle look. Most of the seed plants are big or showy.

Conifers are seed plants; they comprise firs, pines, yew, redwood and most of the other big trees. The other main groups of seed-plants are the flowering plants, comprising plants whose flowers are showy, however as well numerous plants having reduced flowers, like the oaks, Mahogany, palms and grasses.

Classification of Spermatophytes:

The spermatophytes (as well termed as phanerogams) include those plants which produce seeds. They are the subset of embryophytes or land plants. The living spermatophytes make five groups:

a) Cycads, a sub-tropical and tropical group of plants having a big crown of compound leaves and a heavy trunk.

b) Ginkgo, a single living species of the tree,

c) Conifers, shrubs and cone-bearing trees

d) Gnetophytes, woody plants in the genera Gnetum, Ephedra and Welwitschia.

e) Angiosperms, the flowering plants, a big group comprising numerous familiar plants in a broad variety of habitats.

A traditional categorization grouped all the seed plants in a single division having classes for our five groups:

Division Spermatophyta:

  • Cycadopsida, the cycads
  • Ginkgoopsida, the ginkgo
  • Pinopsida, the conifers, (that is, Coniferopsida)
  • Gnetopsida, the Gnetophytes
  • Magnoliopsida, the flowering plants, or Angiospermopsida

Spermatophytes can be broadly classified into two classes namely: Gymnosperms and Angiosperms.

Gymnosperms - naked seed plants:

Gymnosperms symbolize a primitive group of seed bearing plants (that is, Spermatophytes) in which the seeds are naked or nude that is, they are not covered by the fruit wall as in the Angiosperms (The term Gymnos means naked and spermos means seed). The reason is that, in Gymnosperms the ovules are exposed and they are not covered by means of ovary. Rather the ovules are borne directly on the open carpellary leaves termed as megasporophylls and therefore they are naked and they build up into naked seeds after fertilization. The Gymnosperms were most plentiful all through the Mesozoic era (225 million years) ago. Though, they form merely a small portion of the present day vegetation. There are around 70 genera and 900 species of gymnosperms distributed in the tropical and temperate areas. Most of them are Conifers generally evergreen having needle-like leaves. The examples of conifers species are: Pine, Fir, Cedar, Spruce, Gigantia, Cupressus and so on.

Features of Gymnosperms:

1) Gymnosperms are woody perennial that are mostly trees and hardly ever shrubs.

2) The life cycle of gymnosperms exhibits heteromorphic alternation of the generations.

3) They make an intermediate group among Pteridophytes and Angiosperms that is, they are more advanced than Pteridophytes however are primitive than the angiosperms.

4) The plant body is the sporophyte (that is, diploid) generally a tree having well developed stem, roots and leaves.

5) The sporophyte bears two kinds of fertile leaves, the microsporophyll which generates microspores and megasporophylls which generates megaspores.

6) Generally the spores are grouped into compact cones and strobili.

7) Spores on germination build up into gametophytes that are very much reduced, microscopic and based on sporophyte.

8) Seeds are naked and not implanted in fruit.

Classification of Gymnosperms:

Chamberlain has categorized gymnosperms into two groups: Class Cycadophyta and Class Coniferophyta.

The class Cycadophyta comprises of plants having simple stem, thick cortex however thin wood and simple sporophylls. The class Coniferophyta comprises of plants having profusely branched stem, thick wood, thin cortex and complex sporophylls.

Angiosperms - flowering seed plants (covered seed plants)

Angiosperms are plants which encompass seeds encased in the protective covering. That covering is the ovary which is a portion of the flower structure and differentiates angiosperms from gymnosperms. Therefore it can be stated that angiosperms are as well flowering plants. There is one division of angiosperms, Magnoliophyta that is classified into two groups: monocots and dicots. Angiosperms, similar to gymnosperms, are heterosporus that means they produce two kinds of spores and their sporophytes are much dominant than those of gymnosperms.  At maturity, the female gametophytes are decreased to a few cells and are fully enclosed in sporophyte tissue; whereas the male gametophytes comprise of a binucleate cell having a tube nucleus that forms a pollen tube much similar to the one formed in the gymnosperm pollination. 

Relevance of Seed Plants to Humans:

Conifers are the resources for paper products and lumber materials. The resin from conifers has historically been employed as sealing pitch, floor waxes, turpentine, printer's ink, perfumes, menthol manufacture and rosin for the musical instruments. Ginko leaves are employed medicinally. Arrowroot starch was once purified from the cycad species. Teas have been prepared from the conifers. 

Beyond ornamental utilizations, flowering plants comprise much of what we eat, parts of the clothes we wear, the wood in our houses and furniture and the medicines we use.  

Flowering plants are all over and therefore encompass a million uses. All fruit comes from flowering plants, obviously, and assume of how many just in the edible class there is, not to state all of those that are not for eating.

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